1. Department of Sociology, Sungkyunkwan University, Seoul, South Korea.
2. Leonard Davis School of Gerontology, University of Southern California, Los Angeles, CA, USA.
3. Minnesota Population Center, University of Minnesota, Minneapolis, MN, USA.
4. Department of Sociology, University of Minnesota, Minneapolis, MN, USA.
5. Department of Economics, Northwestern University, Evanston, IL, USA.